[Description of Related Art]
Oven controlled crystal oscillator (OCXO; Oven Controlled Crystal Oscillator) includes an oven that keeps a crystal resonator at a constant temperature, and ensures high frequency stability.
The oven controlled crystal oscillator is used for a measuring device of high accuracy and a base station of mobile phones, for example.
[Conventional Oven Controlled Crystal Oscillator: FIG. 11]
A conventional oven controlled crystal oscillator will be described using FIG. 11. FIG. 11 is a sectional drawing illustrating a configuration of a conventional oven controlled crystal oscillator.
As illustrated in FIG. 11, a conventional surface mount device type oven controlled crystal oscillator includes a substrate 1 made of glass epoxy (glass epoxy) or similar material on which an oscillator circuit 2, which includes a crystal resonator, a heater resistor 3, which becomes a heat source, and a power transistor 4, which constitutes a temperature control circuit, are mounted.
Then, the substrate 1 with an electronic part are secured by soldering in a state of floating with a plurality of pins (lead pins) 5 at a predetermined interval above a base 6 made of glass epoxy or similar material, and the substrate 1 is electrically connected to the base 6.
Furthermore, a metal cover 7 is mounted on the base 6 so as to cover the substrate 1 and the electronic parts mounted on the substrate 1, and then sealed, to constitute a package with the base 6 and the cover 7, and a space inside the package forms an oven.
Although a drawing is omitted, a temperature sensor mounted on the substrate 1 detects a temperature inside the oven, and the temperature control circuit including the power transistor 4 controls to maintain the temperature inside the oven constant.
The OCXO maintains the inside at high temperature, which makes a device including the OCXO a heat generating component, and its exhaust heat should be taken into consideration.
For example, generating airflow inside the unit with a fan or similar mechanism to exhaust the heat may be considered.
Accordingly, the peripheral area of the OCXO mounted on the unit is constantly in a state where a wind is blown around the peripheral area, and the heat is drawn from the metal cover 7 of the OCXO.
In this case, the internal temperature drops, thereby a current that flows to the heater resistor 3 and/or the power transistor 4 increases by temperature control.
On the other hand, in the case where the unit is heated with external air rapidly, the heat is transmitted from the outside via the metal cover 7, which may reduce or turn off the current flow to the heater resistor 3.
The OCXO, which is required to be highly stable, may not be allowed to neglect a small frequency variation caused by this slight variation of the current.
[Related Art]
As techniques regarding the oven controlled crystal oscillator, Japanese Unexamined Patent Application Publication No. 2010-56767 discloses “Piezoelectric device apparatus” (NIHON DEMPA KOGYO CO., LTD., Patent Document 1), Japanese Unexamined Patent Application Publication No. 2003-37472 discloses “Composite high-frequency component and radio transmitter-receiver using the same” (HITACHI METALS, LTD., Patent Document 2), Japanese Unexamined Patent Application Publication No. H10-154763 discloses “Container for electronic component and crystal oscillator using the same” (NIHON DEMPA KOGYO CO., LTD., Patent Document 3), and Japanese Unexamined Utility Model Application Publication No. S62-114520 discloses “Piezoelectric oscillator” (NIHON DEMPA KOGYO CO., LTD., Patent Document 4).
Patent Document 1 discloses a piezoelectric device apparatus that includes a first metal case covering a piezoelectric vibrating piece, a second metal case covering the first metal case, and a base plate on which the first metal case and the second metal case are bonded.
Patent Document 2 discloses a composite high-frequency component that includes a piezoelectric crystal body and a metal case covering the piezoelectric crystal body on a multilayer substrate laminated with dielectric layers, and further disposes a second metal case outside the metal case.
Patent Document 3 discloses a configuration for a crystal controlled oscillator including a metal cover on a resin substrate to enhance positional accuracy of the metal cover with respect to the resin substrate by forming a depressed portion on the resin substrate, and forming a leg portion on the metal cover to fit together.
Patent Document 4 discloses a configuration that disposes a heat insulating material inside a resin cover that covers an oven.